The oculomotor reference in humans with bilateral macular disease

Previous studies have shown that most patients with bilateral macular disease use a single retinal area during fixation which is typically located near the edge of the central scotoma. Through frame-by-frame playback of videorecordings showing the target's image on each patient's fundus, we evaluated the sequences of eye movements the patients make during fixation and refixation saccades. We show that although most of our patients with bilateral macular disease had a preferred fixation area, only one third exhibited additional oculomotor behaviors, indicating a complete rereferencing of their eye movements to the preferred area. Such behaviors include the maintenance of the target's image within a circumscribed retinal area during fixation; consistent imaging of the target at the same retinal area as a result of refixation saccades; and the complete absence of "foveating" saccades. Spatial precision of eye movements (fixation and the endpoints of saccades) of patients with a nonfoveal oculomotor reference tends to be scaled to the eccentricity of the preferred fixation area. Saccadic latencies were elevated in patients with bilateral macular disease; elevation was pronounced when the duration of disease was 2 yr or less, but was evident even in patients whose eye movement patterns were consistent with a single nonfoveal reference. We conclude that, over a period of years, a shift of the oculomotor reference from the fovea to a nonfoveal locus is possible in patients with bilateral macular disease. The shift should facilitate the visual rehabilitation of such patients.